1. Field of the Invention
The present invention relates to a recording apparatus for recording video signals and audio signals onto magnetic tape and having editing function of performing assemble editing and insert editing on magnetic tape having signals thus recorded thereon and a reproducing apparatus for reproducing signals from the magnetic tape which has undergone editing function in the recording apparatus.
2. Description of the Prior Art
In recent years, the D-1 format and D-2 format are standardized by the SMPTE for digital VTR's free from degraduation in picture quality and audio quality caused by dubbing. Further, high definition VTR's for recording high-resolution television signals have also been put into practical use. In these digital VTR's and high definition VTR's, a very large number of amount of information must be recorded and high recording density is demanded from the viewpoint of tape consumption, resulting in narrower track pitches (such as 39.1 .mu.m in D-2).
In conventional analog VTR's for broadcast requiring editing function such as VTR's of M2 format or C2 format, it is important to secure the reliability of editing points and a guard is provided between helical tracks. Further, in digital VTR's of D-2 format (as described in "Design Consideration for the D-2 NTSC Composite DVTR" by Richard Brush, SMPTE journal, March 1988), disturbance caused by adjacent tracks is reduced by using a combination of azimuth recording and the Miller.sup.2 channel code. This reduction of disturbance caused by adjacent tracks is owing to the fact that high-frequency components are attenuated by the azimuth effect for crosstalk signals from adjacent tracks and the low frequency energy contained in signals so recorded by means of Miller.sup.2 channel codes as to limit the run length range to 3 data bit cells or less is very little. From these facts, the above described paper says that drift off track of a head by as much as .+-.20 .mu.m or less is in a range wherein correction using an ECC (error-correction coding system) can be performed.
However, this is nothing but a margin for disagreement between a recorded track and the locus of a reproducing head caused when a normally recorded tape is reproduced by another machine. As is well known, track linearities of VTR's differ somewhat with apparatuses. Further, expansion and contraction of tape and/or a servo tracking deviation may be caused with changes in environment. As a result of deviation between a recorded track and the trajectory of a recording head at the time of editing generated by these factors, partial residue of an original recording track which should ideally disappear may be sometimes caused at the editing point in addition to reduction in track width of a track which should be left. Reliability at the editing point must be considered with due regard to these facts.
Assuming now that the tape pattern has a format of a conventional digital VTR using azimuth recording and having no guards between tracks, degradation of the reproduced signal at the editing point will now be described by referring to FIGS. 19A and 19B. In some formats of conventional digital VTR's, audio sectors are disposed at the beginning and the end of helical tracks. For brevity of description, however, the track angle is disregarded and only video sectors are illustrated in FIGS. 19A and 19B. For the same reason, the recording head width is made equal to the track pitch W.sub.p. These figures show a tape pattern obtained when insert editing is performed in a state of tracking deviation (tracking error) and the tape runs from the right to the left. FIGS. 19A and 19B show the tape pattern obtained when an inserted tape pattern (hereafter simply referred to as insert pattern) deviates respectively on the delayed side (i.e., the illustrated right side) and on the advanced side (i.e., the illustrated left side) by W.sub.e with respect to the original tape pattern (hereafter simply referred to as original pattern). PBa and PBb respectively denote positions wherein respective tracks are traced by a wide-width reproduction head having azimuth a and a wide-width reproduction head having azimuth b in the tracking state at the time of recording the original pattern. (Hereafter, tape pattern diagrams are shown in similar forms unless otherwise specified.) When the insert pattern deviates on the delayed side (lag side) by W.sub.e as shown in FIG. 19A, residue of erasing of the original pattern having the same azimuth as that of the leading track of the insert pattern (hereafter referred to simply as residue of the same azimuth) is generated by an amount corresponding to W.sub.e immediately before the in-point as evident from the Figure and the residue is mixed into the reproduction head PBa as disturbance at the time of reproduction. (This phenomenon is hereafter referred to at disturbance of the same azimuth.) Further, as this time, a track width of the original pattern corresponding to the same W.sub.e is shaved at the out point. When the insert pattern is deviated on the advanced side (lead side) (FIG. 19B), a track width of the original pattern immediately before the in-point corresponding to the same W.sub.e is shaved and disturbance due to the residue of the same azimuth corresponding to W.sub.e is caused at the out-point.
When editing is performed in a tape pattern having no guards of the prior art, disturbance due to residue of the same azimuth and reduction in the track width are thus caused. Especially, disturbance due to the residue of the same azimuth corresponds, in case of digital VTR's to degradation in reproduced signal which is 1.5 to 3 times that caused by reduction in track width. IN the case of analog VTR's, disturbance due to the residue of the same azimuth corresponds to degradation in reproduced signal which is several ten times that caused by reduction in track width. (Hereafter, this ratio is referred to as disturbance coefficient of the same azimuth.) A great problem is thus caused.
Further, in case guards are provided as in conventional analog VTR's for broadcast, the track width of all tracks including tracks other than the editing point is largely reduced as compared with the track pitch in the resultant tape format. The disturbance due to the residue of the same azimuth and reduction in the track width as described above pose a great problem in narrow track recording of VGT's needing high-density recording such as high-definition VTR's or digital VTR's.